tests: explicitelty enable drafts for test formdef

This is required after wcs b3eb549 (#12756) as existing drafts won't be
returned if their formdata has drafts disabled.

tests/test_wcs.py

@@ -110,6 +110,7 @@ formdef = FormDef()
 formdef.name = 'third form title'
 formdef.category_id = cats[2].id
 formdef.fields = []
+formdef.enable_tracking_codes = True
 formdef.store()
 
 # a draft of that formdef